1. Field of the Invention
This invention relates to aerial refueling of aircraft from tanker aircraft having a reel-mounted hose and drogue system.
2. Prior Art
Aerial refueling of one aircraft from a flying tanker aircraft has become a fairly common event. One such event was depicted in the recent motion picture entitled “Air Force One.” Nevertheless, aerial refueling is still a difficult and dangerous maneuver and is typically attempted only by military pilots in military aircraft.
Today, two types of aerial refueling systems are used by the various militaries throughout the world. One is an extendible boom system and the other is a hose and drogue system. The invention relates to the latter type system.
In a hose and drogue system, the drogue is attached to the outlet end of a hose. The inlet end of the hose is attached to a reel onto which the hose is wound. The reel is typically mounted either within the tanker aircraft's fuselage or on a refueling pod or module which is attached to the bottom of the tanker aircraft. When the hose is deployed, the outlet end of the hose, with its attached drogue, extends behind the tanker aircraft. Depending upon the combinations of tanker and receiver aircraft and the specifications of the particular refueling system used, the length of the hose may be 50 feet or more, and the drogue is in a preferred refueling range when it is extending about 30 feet from the reel.
When the hose and drogue are in the fully extended position (with several turns of hose still remaining on the reel), the pilot of the aircraft to be refueled maneuvers his or her aircraft into a position such that the refueling probe of the receiver aircraft enters into and engages with the drogue. The pilot continues to urge the receiver aircraft forward relative to the tanker aircraft until the drogue is in the refueling range. As the receiver aircraft is moving forward, the hose is retracted onto the reel to take up the slack in the hose. A refueling range marker is disposed on a predetermined portion of the hose. When the pilot of the receiver aircraft sees the refueling range marker reenter the tanker aircraft's fuselage or refueling pod, the receiver aircraft's pilot knows that the drogue, engaged with the receiver aircraft's probe, is in the refueling range. When the engaged drogue and probe are in the refueling range, fuel is pumped from the tanker aircraft to the receiver aircraft. After refueling is completed, the pilot of the receiver aircraft reduces its speed relative to the tanker aircraft. The hose and drogue are pulled back with the probe of the receiver aircraft, with the hose again being unwound from the reel, until the drogue and hose reach the fully extended position. At this point rotation of the reel stops, the drogue and hose cannot be pulled further back, and the receiver aircraft's refueling probe disengages from the drogue. Retraction of the hose back onto the reel then begins.
Danger arises during the initial engagement from the fact that both the tanker and receiver aircraft are not in locked relationship with each other and the hose (at least at its outlet end) and drogue, once deployed from the tanker aircraft, are not in locked relationship with either aircraft until the refueling probe makes engagement with the drogue. With each of the aircraft traveling at hundreds of miles per hour with respect to the surrounding air, there are a significant number of mis-engagements caused by excessive closing speed between the tanker and receiver aircraft. The frequency of mis-engagements increases with darkness of evening and night. Because the drogue is being hit with considerable force and is being displaced back toward the tanker aircraft before the pilot of the receiver aircraft can reduce the speed of the receiver aircraft to match that of the tanker aircraft, a large amount of slack is formed in the hose and the hose bends into a shape resembling a sine wave.
In this condition, the hose often goes into oscillation with the result that the drogue, “whipping” about, may detach the probe from the receiver aircraft, and the drogue, either itself or with the detached probe, may hit the receiver aircraft causing loss of life and/or of the receiver aircraft.
The hose oscillation problem could be minimized if the hose could be retracted quickly so as to reduce the slack in the hose and to minimize the amplitude of any oscillation resulting from the engagement of the refueling probe and the drogue.
The prior art consists of a hose reel drive assembly which uses a fixed displacement hydraulic motor to control the retraction and extension of the refueling hose, as exemplified by the FR 300 hose reel drive assembly offered for sale by Sargent Fletcher, Inc. of El Monte, Calif. This system does not provide sufficiently quick retraction of the hose and drogue after missed engagements or upon high speed engagements so as to significantly reduce the risks arising therefrom. The principal impediment of the FR 300 hose reel drive assembly and similar systems is the limited hydraulic flow available to hydraulic motors on tanker aircraft. In addition, a fixed displacement hydraulic motor requires a complex hydro-mechanical servo mechanism to control the motor, which increases both its weight and response time.